That Glerk whispers poems to Luna so often makes it clear that he has come to love her. Specifically, the fact that he’s reciting poetry to her shows that he wants her to know all that she possibly can—and introducing her to his poetry is a way for Luna to steep herself in the past and in a different form of storytelling. Xan’s insistence that she can’t make Luna be quiet shows that at this point, sticking to her principles is easy, as noise is a relatively trivial and lighthearted problem.